The present invention relates to the manufacture of refractory articles by casting a fused silica slurry into a mold to form a cast product which is subsequently dried and sintered and, more particularly, to a method of producing such a cast fused silica product having an increased density and reduced porosity whereby improved resistance to chemical attack by metals and slags is imparted to the resultant product.
In the production of metal articles from molten metal, such as aluminum and aluminum alloys, the metal is generally melted in a furnace and conveyed in troughs, lined with a refractory material having good resistance to attack by the molten metal, to a cold core also made of a refractory material having good resistance to attack by the molten metal. It is common practice in industry to form such troughs and molds out of a refractory material formed of fused silica, as, the resultant, cast fused silica is highly pure and will have good resistance to attack by molten metal.
One common method of producing such articles comprises casting a flowable aqueous slurry of fused silica into a plaster of paris mold to form a cast product. The aqueous fused silica slurry is subsequently dried and sintered to provide a resultant product having good resistance to attack by molten metal. The aqueous fused silica slurry is typically formed by subjecting a slurry of fused silica particles in water to wet grinding, typically in a ball mill, to produce an aqueous fused silica slurry wherein the fused silica particles have a particle size less than 325 mesh. Typically, the water content of the resultant fused silica slurry ranges from 18 to 20 percent. Aggregate fused silica particles, typically having a particle size range from -10 to +20 mesh (U.S. standard), are admixed into the aqueous fused silica slurry to increase the solids content of the resultant casting mix and to permit a lower porosity, higher density product to be obtained. It is a well known fact that the higher the water content in the casting mix, the higher the porosity and the lower the density of the resultant casted product. Therefore, it is well appreciated that when casting an aggregate mix, it is desirable to have the lowest possible water content in order to produce a product having high density and low porosity. However, it is also a known fact that if the casting mix contains too high a content of aggregate fused silica paticles, the casting mix becomes too sandy and will not flow properly, thereby, making mold filling difficult. Consequently, when using a high purity, fused silica slurry for casting such products, the density of the resultant article has been limited to approximately 120 pounds/cubic foot or less and the porosity of the resultant article has been limited to approximately 13% or more.
Accordingly, it is an object of the present invention to provide a method for producing, by casting, high purity fused silica articles having a density in excess of about 125 pounds/cubic foot and a porosity of less than about 10%; this density and porosity, and all density or porosity values referred to herein, being calculated in accordance with the procedures described at pages 31 and 32 of a book entitled "CERAMIC TESTS AND CALCULATIONS", by Andrew I. Andrews, published by John Wiley & Sons, 1950, 8th printing.